Method for communicating encoded traffic indication map
information

ABSTRACT

Provided is a method of communicating encoded traffic indication map (TIM) information that can reduce power consumption by reducing an unnecessary decoding process. A method of receiving, by a terminal, a TIM that is encoded in a hierarchical structure including a page, a block, and a sub-block includes receiving an encoded TIM from an access point (AP), extracting a page index from the encoded TIM, and extracting block bitmap information indicating whether blocks included in a page designated by the page index include a bitmap. Therefore, an unnecessary decoding process with respect to each delivery traffic indication map (DTIM) beacon can be reduced, thereby reducing power consumption of a low-power terminal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. patent application Ser. No. 14/406,576,filed Dec. 9, 2014, which is a National Stage Application ofPCT/KR2013/005104 filed Jun. 11, 2013, and claims priority from KoreanApplication No. 10-2013-0025959 filed Mar. 12, 2013 and KoreanApplication No. 10-2012-0063372 filed Jun. 13, 2012. The entiredisclosures of the prior applications are considered part of thedisclosure of the accompanying continuation application, and are herebyincorporated by reference in their entireties.

TECHNICAL FIELD

The present invention relates to wireless communication technology, andmore particularly, to a method of communicating encoded trafficindication map (TIM) information that can reduce power consumption byreducing an unnecessary decoding process.

BACKGROUND ART

With the development of information communication technologies, avariety of wireless communication technologies have been developed.Among these technologies, wireless local area network (WLAN) is atechnology that Internet access is possible in a wireless way in homes,business or specific service providing areas, using portable terminalsuch as personal digital assistant (PDA), a laptop computer, a portablemultimedia player (PMP), or the like, based on wireless frequencytechnologies.

WLAN technologies is created and standardized by the IEEE 802.11 WorkingGroup under IEEE 802 Standard Committee. IEEE 802.11a provides a maximumPHY data rate of 54 Mbps using an 5 GHz unlicensed band. IEEE 802.11bprovides a maximum PHY data rate of 11 Mbps by applying a directsequence spread spectrum (DSSS) modulation at 2.4 GHz. IEEE 802.11gprovides a maximum PHY data rate of 54 Mbps by applying orthogonalfrequency division multiplexing (OFDM) at 2.4 GHz. IEEE 802.11n providesa PHY data rate of 300 Mbps using two spatial streams and bandwidth of40 MHz, and provides a PHY data rate of 600 Mbps using four spatialstreams and bandwidth of 40 MHz.

As such WLAN technology becomes more prevalent and its applicationsbecome more diverse, there is increasing demand for new WLAN technologythat can support a higher throughput than IEEE 802.11n. Very highthroughput (VHT) WLAN technology, that is one of the IEEE 802.11 WLANtechnologies, is proposed to support a data rate of 1 Gbps and higher.IEEE 802.11ac has been developed as a standard for providing VHT in the5 GHz band, and IEEE 802.11ad has been developed as a standard forproviding VHT in the 60 GHz band.

In a system based on such WLAN technology, an access point (AP) setsbits corresponding to an association ID (AID) of each terminal in abitmap control and a partial virtual bitmap among traffic indication map(TIM) elements of a beacon when there is data to be transmitted to theterminal, whereby the terminal can determine whether there is data to betransmitted.

Since a length field of a TIM element format has 1 octet, the partialvirtual bitmap may have up to a maximum of 251 octets, and therefore atotal of 2007 terminals (8251-1) can be expressed.

Meanwhile, in order to express and manage at least 2007 terminals as aTIM bitmap, a method of encoding the TIM bitmap in units of blocks whilehaving a hierarchical AID structure has been proposed.

Here, a page ID is displayed in an existing bitmap control, and encodedbitmap blocks are continuously displayed in units of blocks in thepartial virtual bitmap.

In addition, a single encoded bitmap block includes a block control of 3bits, a block offset of 5 bits, a fixed length part of 2 octetsincluding a block bitmap of 1 octet, and a sub-block bitmap part havinga variable length.

However, in order for a terminal in an N-th block (N is a natural numbergreater than 1) to determine whether a TIM bit of the terminal is set, aposition of a block control of the N-th block has to be found, and anactual position of the bitmap has to be determined in accordance with ablock encoding mode. In addition, since each block has a variablelength, a position of an N-th block control cannot be found from a fixedposition, and blocks from a first block to an (N−1)-th block have to besequentially decoded.

That is, when there is actual data to be transmitted, bitmaps of allblocks should be all decoded, but in an environment in which a smallamount of data is intermittently transmitted, such as a sensor network,there is a problem in that all blocks have to be decoded with respect toall delivery traffic indication map (DTIM) beacons in order to determinethe presence or absence of data even though there is no data.

DISCLOSURE Technical Problem

The present invention is directed to providing a method of receivingencoded traffic indication map (TIM) information that can reduce powerconsumption by reducing an unnecessary decoding process.

The present invention is also directed to providing a method oftransmitting encoded TIM information that can reduce power consumptionby reducing an unnecessary decoding process.

Technical Solution

One aspect of the present invention provides a method of receiving, by aterminal, a traffic indication map (TIM) that is encoded in ahierarchical structure including a page, a block, and a sub-block, themethod including: receiving an encoded TIM from an access point (AP);extracting a page index from the encoded TIM; and extracting blockbitmap information indicating whether blocks included in a pagedesignated by the page index include a bitmap.

Here, the block bitmap information may be positioned before bitmapinformation designating the block or the sub-block within the encodedTIM.

In addition, the method may further include decoding, when bits fordesignating a block including an association ID (AID) of the terminalare set in the extracted block bitmap information, a bitmap of the blockincluding the AID of the terminal.

In addition, the method may further include stopping, when bits fordesignating a block including an AID of the terminal are not set in theextracted block bitmap information, decoding of a bitmap designating theblock or the sub-block.

In addition, when the bits for designating the block including the AIDof the terminal are not set in the extracted block bitmap information,the terminal may enter a power save mode without decoding the bitmap fordesignating the block or the sub-block.

Another aspect of the present invention provides a method oftransmitting, by an AP, a TIM that is encoded in a hierarchicalstructure including a page, a block, and a sub-block, the methodincluding: generating block bitmap information for designating whetherblocks included in a page designed by a page index include a bitmap;generating a TIM including the page index and the block bitmapinformation; and transmitting the TIM to a terminal.

Here, the block bitmap information may be positioned before bitmapinformation for designating the block or the sub-block within theencoded TIM.

Advantageous Effects

According to the above-described method of communicating an encodedtraffic indication map (TIM) information according to an embodiment ofthe present invention, a page index can be extracted from an encoded TIMreceived from an access point (AP), block bitmap information indicatingwhether blocks included in a page designated by the page index include abitmap can be extracted, and then whether decoding can be performed inaccordance with the bits for designating a block including anassociation ID (AID) of the terminal are set in the extracted blockbitmap information can be determined in advance.

Accordingly, it can be determined whether decoding of the entire TIM mapis performed by reading only a block bitmap part of a delivery trafficindication map (DTIM) beacon. Therefore, it is possible to reduce powerconsumption of the terminal by reducing an unnecessary decoding processwith respect to each DTIM beacon.

DESCRIPTION OF DRAWINGS

FIG. 1 shows a traffic indication map (TIM) element format of a beacon;

FIG. 2 shows a hierarchical association ID (AID) structure;

FIG. 3 shows an encoded TIM in units of blocks;

FIG. 4 shows TIM bitmap encoding in units of blocks in which a blockbitmap of 4 octets is added according to an embodiment of the presentinvention;

FIG. 5 shows a TIM encoding mode that adds a block bitmap of 4 octetsand uses a common block control field according to an embodiment of thepresent invention;

FIG. 6 is a flowchart showing a method of receiving encoded TIMinformation according to an embodiment of the present invention;

FIG. 7 is a flowchart showing a method of transmitting encoded TIMinformation according to an embodiment of the present invention.

MODE FOR INVENTION

Hereinafter, exemplary embodiments of the present invention will bedescribed in detail. However, the present invention is not limited tothe exemplary embodiments disclosed below, but can be implemented invarious forms. The following exemplary embodiments are described inorder to enable those of ordinary skill in the art to embody andpractice the invention.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another. For example, a first element could be termed asecond element, and, similarly, a second element could be termed a firstelement, without departing from the scope of the present invention. Asused here, the term and/or includes any and all combinations of one ormore of the associated listed items.

It will be understood that when an element is referred to as beingconnected or coupled to another element, it can be directly connected orcoupled to the other element or intervening elements may be present. Incontrast, when an element is referred to as being directly connected ordirectly coupled to another element, there are no intervening elementspresent.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms a, an and the are intended to includethe plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms comprises,comprising, includes and/or including, when used herein, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. It will befurther understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined here.

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with the accompanying drawings. In the followingdescription, the same reference numerals denote the same elements tofacilitate the overall understanding, and repeated description thereofwill be omitted.

In the specification, station (STA) denotes an arbitrary functionalmedium including a medium access control (MAC) layer defined byinstitute of Electrical and Electronics Engineers (IEEE) 802. 11standard, and a physical layer interface with respect to a wirelessmedium. STAs may be divided into STAs that are access points (APs) andSTAs that are not APs. An STA that is an AP may be simply referred to asan AP, and an STA that is not an AP may be simply referred to as aterminal. The terminal may include a processor and a transceiver, andmay further include a user interface, a display device, and the like.The processor denotes a unit that is designed to generate a frame to betransmitted through a wireless network or process a frame receivedthrough the wireless network, and performs a variety of functions forcontrolling the station (STA). The transceiver may be functionallyconnected with the processor, and denotes a unit that is designed totransmit and receive a frame through the wireless network for the STA.

The AP may refer to a centralized controller, a base station (BS), aNode-B, an eNode-B, a base transceiver system, a site controller, or thelike, and may include some or all functions thereof.

The terminal may refer to a wireless transmit/receive unit (WTRU), userequipment (UE), a user terminal (UT), an access terminal (AT), a mobilestation (MS), a mobile terminal, a subscriber unit, a subscriber station(SS), a wireless device, a mobile subscriber unit, or the like, and mayinclude some or all functions thereof.

Here, the terminal may be a desktop computer enabling communication, alaptop computer, a tablet PC, a wireless phone, a mobile phone, a smartphone, an e-book reader, a portable multimedia player (PMP), a portablegame console, a navigation device, a digital camera, a digitalmultimedia broadcasting (DMB) player, a digital audio recorder, adigital audio player, a digital picture recorder, a digital pictureplayer, a digital video recorder, a digital video player, or the like.

A method of communicating encoded traffic indication map (TIM)information according to an embodiment of the present invention, whichwill be described later, may be applied to the above-described IEEE802.11 wireless local area network (WLAN) system. It may further beapplied to a variety of networks such as a wireless personal areanetwork (WPAN), a wireless body area network (WBAN), and the like, aswell as the IEEE 802.11 WLAN system.

FIG. 1 shows a traffic indication map (TIM) element format of a beacon,FIG. 2 shows a hierarchical association ID (AID) structure, and FIG. 3shows an encoded TIM in units of blocks.

Referring to FIGS. 1 to 3, a TIM element format of a beacon in a WLANsystem includes an element ID, a length, a delivery traffic indicationmap (DTIM) count, a DTIM period, a bitmap control, and a partial virtualbitmap.

An access point (AP) may set bits corresponding to an association ID(AID) of each terminal in the bitmap control and the partial virtualbitmap among the TIM elements of the beacon when there is data to betransmitted to a terminal, thereby indicating the presence of the datato be transmitted to the terminal.

Since a length field of the TIM element format has 1 octet, the partialvirtual bitmap may have up to a maximum of 251 octets, and therefore atotal of 2007 terminals (8251-1) can be expressed.

In addition, in order to express and manage at least 2007 terminals as aTIM bitmap, a method of encoding the TIM bitmap in units of blocks asshown in FIG. 3 while having a hierarchical AID structure shown in FIG.2 has been proposed.

Specifically, referring to FIG. 3, in the proposed method of encodingthe TIM bitmap in units of blocks, a page ID is displayed in an existingbitmap control, and encoded bitmap blocks are continuously displayed inunits of blocks in the partial virtual bitmap.

In addition, a single encoded bitmap block includes a block control of 3bits, a block offset of 5 bits, a fixed length part of 2 octetsincluding a block bitmap of 1 octet, and a sub-block bitmap part havinga variable length. Here, a block control field controls uses of theblock bitmap and the sub-block bitmap field.

In addition, the block offset represents an offset value of a block.

In addition, the block bitmap represents a position bitmap of thesub-block on which AID bit setting is performed.

In addition, the sub-blocks represent a position bitmap of an AID withinthe sub-block.

In order for a terminal in an N-th block (N is a natural number greaterthan 1) to determine whether a TIM bit of the terminal is set, aposition of a block control of the N-th block has to be found, and anactual position of the bitmap has to be determined in accordance with ablock encoding mode.

In addition, since each block has a variable length, a position of anN-th block control cannot be found from a fixed position, and blocksfrom a first block to an (N−1)-th block have to be sequentially decoded.

That is, when there is actual data to be transmitted, bitmaps of allblocks should be all decoded, but in an environment in which a smallamount of data is intermittently transmitted, such as a sensor network,there is a problem in that all blocks have to be decoded with respect toall delivery traffic indication map (DTIM) beacons in order to determinethe presence or absence of data, even though there is no data.

Hereinafter, in order to solve the above-described problem, anembodiment of the present invention in which a terminal can determinethat there is no data to be transmitted to the terminal, through only apart of TIM elements of a DTIM beacon, to thereby stop additionaldecoding, will be described with reference to the drawings.

FIG. 4 shows TIM bitmap encoding in units of blocks in which a blockbitmap of 4 octets is added according to an embodiment of the presentinvention, and FIG. 5 shows a TIM encoding mode that adds a block bitmapof 4 octets and uses a block control field according to an embodiment ofthe present invention.

Referring to FIGS. 4 and 5, an embodiment of the present invention addsa block bitmap of 4 octets to a TIM bitmap.

That is, a terminal may primarily determine whether overall decoding ofthe block bitmap of the TIM element is performed based on a block indexincluding of an AID of the terminal.

Here, the block bitmap refers to a bitmap corresponding to offset ofblocks including an AID of a terminal to which data is transmitted.

In addition, the block bitmap is positioned before bitmap informationdesignating a block or a sub-block within an encoded TIM.

Specifically, referring to FIG. 4, a TIM bitmap according to anembodiment of the present invention may be encoded in units of blocks, apage ID may be displayed in an existing bitmap control, and a blockbitmap for displaying whether encoding of a specific block is performedand encoded bitmap blocks encoded in units of blocks may be continuouslydisplayed in the partial virtual bitmap.

In addition, a single encoded bitmap block includes a block control of 3bits, a block offset of 5 bits, a fixed length part of 2 octetsincluding a block bitmap of 1 octet, and a sub-block bitmap part havinga variable length. Here, a block control field controls uses of theblock bitmap and the sub-block bitmap field.

In addition, the block offset represents an offset value of a block.

In addition, the sub-block bitmap represents a position bitmap of asub-block on which AID bit setting is performed.

In addition, the sub-blocks represent a position bitmap of an AID withina sub-block.

Specifically, referring to FIG. 5, a TIM bitmap according to anembodiment of the present invention may be encoded in units of blocks, apage ID and a block control may be included in an existing bitmapcontrol, and a block bitmap for displaying whether encoding of aspecific block is performed and encoded bitmap blocks encoded in unitsof blocks may be continuously displayed in the partial virtual bitmap.

In addition, a single encoded bitmap block includes a sub-block bitmaphaving a fixed length of 1 octet and sub-blocks having a variablelength.

Here, the block control has a length of 3 bits and controls encoding ofthe sub-block bitmap and the sub-blocks.

In addition, the sub-block bitmap represents a position bitmap of asub-block on which AID bit setting is performed.

In addition, the sub-block represents a position bitmap of an AID withina sub-block.

Specifically, a terminal may receive an encoded TIM from an AP, andfirst extract block bitmap information from the received encoded TIM,thereby determining whether bits for designating an encoded bitmap blockincluding an AID of the terminal are set.

When the bits for designating the encoded bitmap block including the AIDof the terminal are set in the extracted block bitmap information, theterminal decodes a bitmap of the encoded bitmap block including the AIDof the terminal.

Alternatively, when the bits for designating the encoded bitmap blockincluding the AID of the terminal are not set in the extracted blockbitmap information, the terminal stops bitmap decoding of the encodedbitmap block for designating the block or the sub-block.

In addition, when the overall encoding blocks can be used in the samemode, a block control field and a block offset field of each of theencoded blocks may be omitted, as shown in FIG. 5.

According to an embodiment of the present invention, a terminal mayextract block bitmap information from an encoded TIM received from theAP, and stop bitmap decoding of the encoded bitmap block for designatingthe block or the sub-block when bits for designating the encoded bitmapblock including the AID of the terminal are not set in the extractedblock bitmap information, thereby reducing power consumption of thelow-power terminal.

FIG. 6 is a flowchart showing a method of receiving encoded TIMinformation according to an embodiment of the present invention.

Referring to FIG. 6, in step S610, a terminal according to an embodimentof the present invention receives an encoded TIM from an AP.

In step S620, the terminal extracts a page index from the encoded TIMreceived through step S610.

Next, in step S630, the terminal extracts block bitmap informationindicating whether blocks included in a page designated by the pageindex extracted through step S620 include a bitmap.

Here, the block bitmap information is positioned before bitmapinformation for designating a block or a sub-block within the encodedTIM.

In step S640, the terminal determines whether bits for designating anencoded bitmap block including an AID of the terminal are set in theextracted block bitmap information.

In step S650, when the bits for designating the encoded bitmap blockincluding the AID of the terminal are set in the block bitmapinformation extracted through step S640, the terminal decodes a bitmapof the encoded bitmap block including the AID of the terminal.

Alternatively, in step S660, when the bits for designating the encodedbitmap block including the AID of the terminal are not set in the blockbitmap information extracted through step S640, the terminal does notdecode the bitmap of the encoded bitmap block for designating the blockor the sub-block.

In addition, in step S670, the terminal enters a power save mode withoutdecoding the bitmap of the encoded bitmap block for designating theblock or the sub-block through step S660.

Here, in steps S660 and S670, for convenience of description, thestopping decoding of the bitmap of the encoded bitmap block fordesignating the block or the sub-block is first performed, but stepsS660 and S670 may be performed in forward order, reverse order, orsimultaneously.

According to the method for receiving encoded TIM information accordingto an embodiment of the present invention, the block bitmap informationis positioned before the bitmap information for designating the block orthe sub-block within the encoded TIM, and therefore, when bits fordesignating the encoded bitmap block including the AID of the terminalare not set in the block bitmap information, decoding of the bitmap ofthe encoded bitmap block for designating the block or the sub-block maystop, thereby reducing power consumption of a low-power terminal.

FIG. 7 is a flowchart showing a method of transmitting encoded TIMinformation according to an embodiment of the present invention.

Referring to FIG. 7, in step S710, an AP generates block bitmapinformation for designating whether blocks included in a page designatedby a page index include a bitmap.

Here, the block bitmap information is positioned before bitmapinformation for designating a block or a sub-block within an encodedTIM, so that a terminal can determine whether there is data to betransmitted to the terminal through only a front part of TIM elements ofa DTIM beacon.

In step S720, the AP generates a TIM including the page index and theblock bitmap information generated through step S710.

Next, in step S730, the AP transmits the TIM generated through step S720to the terminal.

According to the method of transmitting the encoded TIM informationaccording to an embodiment of the present invention, the block bitmapinformation is positioned before the bitmap information for designatingthe block or the sub-block within the encoded TIM, and therefore, whenbits for designating the encoded bitmap block including the AID of theterminal are not set in the block bitmap information, decoding of thebitmap of the encoded bitmap block for designating the block or thesub-block may stop, thereby reducing power consumption of a low-powerterminal.

In this specification, in order to be concise, exemplary embodiments ofthe present invention have been classified into the first, second andthird exemplary embodiments. However, steps or functions of an exemplaryembodiment may be combined with those of another exemplary embodiment toimplement still another exemplary embodiment of the present invention.

While the invention has been shown and described with reference tocertain exemplary embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims.

1. A method for processing a beacon frame by a terminal in a wireless local area network, the method comprising: receiving, by the terminal from an access point (AP), the beacon frame including a traffic indication map (TIM), a first bitmap and one or more second bitmap, wherein: the TIM is based on a hierarchical structure that a page includes a plurality of blocks and a block includes a plurality of sub-blocks, and the first bitmap indicates presence of buffered data for each of one or more blocks, a second bitmap indicates presence of buffered data for each of one or more sub-blocks, and a sub-block indicates whether there is data for each of one or more terminals; and decoding the one or more blocks when the first bitmap indicates that there is a buffered data at the AP for the terminal.
 2. The method according to claim 1, wherein the one or more blocks are not decoded by the terminal when the first bitmap indicates that there is no buffered data at the AP for the terminal.
 3. The method according to claim 1, wherein the terminal enters a power save mode immediately when the first bitmap indicates that there is no buffered data at the AP for the terminal.
 4. The method of claim 1, wherein a maximum length of the first bitmap is 4 octets.
 5. A method of transmitting a beacon frame by an access point (AP) in a wireless local area network, the method comprising: generating the beacon frame including a traffic indication map (TIM), a first bitmap and one or more second bitmap, wherein: the TIM is based on a hierarchical structure that a page includes a plurality of blocks and a block includes a plurality of sub-blocks, and the first bitmap indicates presence of buffered data for each of one or more blocks, a second bitmap indicates presence of buffered data for each of one or more sub-blocks, and a sub-block indicates whether there is data for each of one or more terminals; and transmitting the beacon frame, wherein the one or more blocks are decoded by a terminal when the first bitmap indicates that there is a buffered data at the AP for the terminal.
 6. A terminal for processing a beacon frame in a wireless local area network, the terminal comprising: a transceiver; and a processor, wherein the processor is configured to: receive, from an access point (AP), the beacon frame including a traffic indication map (TIM), a first bitmap and one or more second bitmap, wherein: the TIM is based on a hierarchical structure that a page includes a plurality of blocks and a block includes a plurality of sub-blocks, and the first bitmap indicates presence of buffered data for each of one or more blocks, a second bitmap indicates presence of buffered data for each of one or more sub-blocks, and a sub-block indicates whether there is data for each of one or more terminals; and decode the one or more blocks when the first bitmap indicates that there is a buffered data at the AP for the terminal.
 7. An access point (AP) for transmitting a beacon frame in a wireless local area network, the AP comprising: a transceiver; and a processor, wherein the processor is configured to: generate the beacon frame including a traffic indication map (TIM), a first bitmap and one or more second bitmap, wherein: the TIM is based on a hierarchical structure that a page includes a plurality of blocks and a block includes a plurality of sub-blocks, and the first bitmap indicates presence of buffered data for each of one or more blocks, a second bitmap indicates presence of buffered data for each of one or more sub-blocks, and a sub-block indicates whether there is data for each of one or more terminals; and transmit the beacon frame, wherein the one or more blocks are decoded by a terminal when the first bitmap indicates that there is a buffered data at the AP for the terminal. 